Siemens 3UG4 User Manual page 24

System overview
3.3 Connection methods
The devices are equipped with a two-wire terminal, i.e. two independent connections for
each current path (exception: in the case of 3RR2, terminals of the main current paths have
one clamping point). Just one conductor is connected to each clamping point. The spring-
loaded terminal presses the conductor against the busbar, which curves around inside the
terminal. The high contact pressure per unit area achieved in this way is gas-tight. The
spring-loaded terminal presses flat against the conductor, but does not damage it. The
spring force of the spring-loaded terminal has been dimensioned such that the clamping
force adjusts to the conductor diameter automatically. This ensures that any conductor
deformation caused by settling, creepage, or yielding is compensated for. The clamping
point cannot become loose of its own accord. This connection is vibration- and shock-proof.
Vibrations or shocks will not damage the conductor, nor will they cause contact separation.
These terminals are particularly well suited for use with machines and systems which are
subject to stresses such as these, e.g. vibrators, rail vehicles, and elevators.
The contact pressure between the conductor and the busbar is set to an optimum level, so
this clamp connection is appropriate for high-voltage applications, as well as for transferring
voltages and currents in the mV or mA range within instrumentation and electronic
components.
A standardized screwdriver (3 mm slot; 3RA2908-1A) is offered in the Catalog IC10
"Industrial Controls" (www.siemens.com/industrial-controls/catalogs) as an actuation tool for
opening the spring-loaded terminals.
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3UG4 / 3RR2 monitoring relays
Manual, 05/2016, NEB927043002000/RS-AC/004